Starch extraction and modification from raw grain and tuber products is one of the biggest markets in the food, animal feed and industrial starch industries internationally. Each day, thousands of tonnes of starch-based products are processed to extract the starch from it, before converting it to a variety of starch powders, premixes, pastes or liquids for use, inter alia, in beer production, meat and fish products, confectionery, jams and preserves, syrups, paper and cardboard manufacturing, animal and aqua feeds, pet food and many other related applications.
Production of the diverse range of starch-based products requires dedicated adherence to prescribed manufacturing procedures, which often include interventions with substantially noxious and potentially caustic chemical agents for specific manipulation of the molecular features and characteristics of both in-process and end-product starch molecules. These interventions are specifically designed to result in the production of different end products with highly specific and differentiated molecular configurations, which then confer specific and predictable performance when combined in further manufacturing procedures.
These chemical interventions include biocidal remedies to restrict the presence of pathogenic and spoilage micro-organisms which directly impact on the biosecurity of the product produced and thus the capacity to comply with internal as well as customer batch specifications. Optimal decontamination of these starch-based products is a critical factor in determining final product quality, not only from an economic perspective, but particularly from a human and animal safety perspective.
For purposes of this specification, the terms “starch source” or “starch-based products” should be interpreted to include tubers (e.g. potatoes), grains, tapioca and derivative products (e.g. partially processed grains). “Grains” should be interpreted to include nuts, oil seeds, barley, wheat, maize (e.g. waxy and high amylose maize), rye, oats, corn and grains of any other cereal crops from which starch can be extracted.
Industrial Treatment of Starch-Based Products
Industrial starch production encompasses a diverse array of processing procedures for an extensive variety of starch types, all geared towards the production of either pure or derivative starch based products which have been tailored to specific applications and inclusions.
In the grain malting industry, graded barley grains undergo repeated immersion in steep water to increase moisture content from approximately 14% to around 45%. Germination of the embryo within the barley kernel is initiated at around 35% moisture content and the moistened grain is “germinated” for up to 6 days to form what is known as ‘green malt’. This process facilitates optimal enzymatic modification of the starch in the endosperm, but requires termination prior to the endosperm being converted into a starch source required for the developing roots and leaf shoots. Control of the process depends largely on the optimisation of the quality and quantity of the steeping water, the exclusion of overgrowth of microbial contaminants, and the maintenance of optimal temperature and humidity of the germinating grains during the development of the ‘green malt’. Treatment of steep water with biocidal agents to preclude microbial growth and mycotoxin generation must be balanced against the potential adverse impact upon the germinating grains as well as the potential for chemical taint of the starch undergoing enzymatic modification. Thus, water quality remains a critical component for the efficient production of a fundamental ingredient in the brewing process.
In an industrial starch mill, a new shipment of starch-based products is first graded according to, inter alia, colour, size, level of superficial microbial and mycotoxin contamination, and moisture, oil and protein content, after which the starch-based products are weighed and cleaned in a preliminary first stage screening process to remove dust, chaff and foreign materials. The starch-based products are subsequently conveyed to steeping vessels where they undergo steeping in lukewarm steepwater, essentially to permit optimal germ extraction and mobilisation of the endosperm. During steeping these grain products absorb water, which results in softening of the grain husks and an elevation of the moisture level and size of the kernels.
Sulfur dioxide (SO2) is generally added to the steepwater to prevent excessive bacterial growth in this warm environment. The mild acidity of the steepwater also begins to loosen gluten bonds within the starch-based products, thereby initiating the mobilising of the starch molecules.
The softened husks are removed and the grain is coarsely ground to break the grain germ, also known as the embryo, loose from other components, such as the endosperm and fiber. The ground grain is carried in a water slurry to cyclone germ separators where the low density germ is spun out of the slurry and retained for further processing, e.g. extraction of oils, while the germ residue may be used in animal feeds.
The starch-based products undergo a second, more severe grinding stage to release the starch and gluten from the fiber in the kernel. The starch and gluten, which is now referred to as “mill starch”, is separated from the fiber and conveyed to starch separators, while the fiber may be treated further for use in animal feeds. The mill starch slurry is passed through a separator, such as a centrifuge, to separate the low density gluten from the starch. The gluten may be used in animal feeds. The starch slurry is diluted and repeatedly washed to remove any remaining protein traces. The starch slurry is then dried to about 12% moisture content and either (i) sold as unmodified starch; (ii) converted into syrups and dextrose; or (iii) chemically modified into specialty starches by applying different reagents, heat and pressure to change the properties of the unmodified starch.
One of the difficulties associated with starch separation processes concerns the addition of SO2 to the steepwater during conditioning. Although SO2 may be a good bacteriostat, it is harmful to humans and can result in severe respiratory conditions. Accordingly, special precautionary measures are required in starch processing facilities to provide for the step of SO2 addition. Also, microbial contaminants tend to become tolerant after exposure to continuously consistent levels of SO2, which may decrease the antimicrobial efficacy of SO2 over time. Finally, SO2 may also impart an adverse colour taint to the intermediate and final product, thus requiring an intervention with potent oxidising agents to both neutralise its activity as well as to diminish the associated colour taint.
Moreover, after steeping, it is necessary to eliminate any traces of SO2 before further processing of the starch slurry, especially where it is intended for human or animal consumption applications. This is usually done by adding an oxidant, notably a peroxide composition such as benzoyl peroxide, to the mill starch slurry for neutralisation of the sulfur dioxide.
However, peroxide is an expensive chemical, which increases production costs. In addition, peroxide is highly corrosive in nature, which not only damages process equipment over time, but also complicates material handling protocols in a starch separation process. Moreover, once peroxide is added to the mill starch, any bacteriostatic efficacy of SO2 is eliminated, hence creating substantial opportunity for microbial and specifically fungal proliferation and consequential spoilage with an increased potential for mycotoxin generation during downstream processing of the mill starch slurry.
One of the ways in which to modify starches chemically involves reducing the size of a starch polymer through oxidation. This is achieved by mixing sodium hypochlorite (NaOCl) into a starch slurry. Sodium hypochlorite cleaves the complex linkages within a starch polymer, as well as the carbon-to-carbon bonds in a dextrose molecule, to produce large carboxyl and carbonyl groups. These groups reduce the tendency of starch to retrograde, give the starch a stickiness that is beneficial for coating foods and in batters, and make the starches more stable.
Electrochemically Activated Aqueous Compositions
It is well known that production of electrochemically activated (ECA) solutions from diluted dissociative salt solutions involves passing an electrical current through an electrolyte solution in order to produce separable catholyte and anolyte solutions. Those who are engaged in the industry will appreciate that catholyte, which is the solution exiting the cathodal chamber, is an anti-oxidant and normally has a pH in the range of from about 8 to about 13, and an oxidation-reduction (redox) potential (ORP) in the range of from about −200 mV to about −1100 mV. The anolyte, which is the solution exiting the anodal chamber, is an oxidant and is generally an acidic solution with a pH in the range from about of between 2 and to about 8, an ORP in the range of from about +300 mV to about +1200 mV, and a Free Active Oxidant concentration of ≦300 ppm.
During electrochemical activation of aqueous electrolyte solutions, various oxidative and reductive species are present in solution, for example HOCl (hypochlorous acid); ClO2 (chlorine dioxide); ClO2− (chlorite); ClO3− (chlorate); ClO4− (perchlorate); OCl− (hypochlorite); Cl2 (chlorine); O2 (oxygen); H2O2 (hydrogen peroxide); OH− (hydroxyl); and H2 (hydrogen). The presence or absence of any particular reactive species in solution is predominantly influenced by the derivative salt and the final solution pH. So, for example, at pH 3 or below, HOCl converts to Cl2, which increases toxicity levels. At pH below 5, low chloride concentrations produce HOCl, but high chloride concentrations will produce Cl2 gas. At pH above 7.5, hypochlorite ions (OCl−) are the dominant species. At pH>9, the oxidants (chlorites, hypochlorites) convert to non-oxidants (chloride, chlorates and perchlorates) and active chlorine (i.e. defined as Cl2, HOCl and ClO−) is lost due to the conversion to chlorate (ClO3−). At a pH of 4.5-7.5, the predominant species are HOCl (hypochlorous acid), O3 (ozone), O22− (peroxide ions) and O2− (superoxide ions).
For this reason, anolyte predominantly comprises species such as ClO; ClO−; HOCl; OH−; HO2; H2O2; O3; S2O82− and Cl2O62−, while catholyte predominantly comprises species such as NaOH; KOH; Ca(OH)2; Mg(OH)2; HO−; H3O2−; HO2−; H2O2−; O2−; OH− and O22−. The order of oxidizing power of these species is: HOCl (strongest)>Cl2>OCl− (least powerful). For this reason anolyte has a much higher antimicrobial and disinfectant efficacy in comparison to that of catholyte or commercially available stabilized chlorine formulations when used at the recommended dosage rates.